Display devices such as liquid crystal displays and organic light emitting diode displays, portable transmitting devices, and other information processing devices use various input devices to perform functions. Recently, one such input device, the touch screen device has been widely employed in mobile phones, smart phones, palm-size PCs, automated teller machines (ATMs), etc.
A finger, touch pen, stylus, etc. is used to contact the screen of a touch screen device to write characters, draw pictures, or execute an icon to perform a desired command.
Such touch screen devices can be categorized largely into resistive type and capacity type touch screen devices, depending on the method of sensing a touch.
A resistive type touch screen device has a structure in which a resistive material is coated on a glass or transparent plastic plate, over which a polyester film is then coated. Insulating rods are installed at uniform distances apart so as not to touch one another, between two surfaces of a resistive type touch screen device. Resistance changed by a touch on the screen changes voltage, which is detected to sense the touched position. A resistive type touch screen device has the drawback of being unable to sense a touch if the pressure is too light.
Conversely, a capacitive type touch screen device includes electrodes formed on one or both sides of glass or transparent plastic. A voltage is applied between two electrodes, and when a finger or other object contacts the screen, the variation in capacitance between the two electrodes is analyzed to sense the touched point.
A capacitive type touch screen device requires a sensing circuit to measure the capacitance formed between two electrodes in order to sense a touched point. A sensing circuit used in the touch screen device of a mobile phone or the like measures the variation in a capacitor formed between two electrodes of a touch screen panel. A method is required for increasing the variation in a capacitor in order to improve the sensing performance of a touch screen device.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.